1. Field of the Invention
This invention relates to a stereo-observation system which is suitable for stereoscopic observation on left and right images with parallax, formed by a stereo imaging apparatus, such as a stereo endoscope, having a wide range of depth of field.
2. Description of Related Art
In recent years, the technique of using the stereo-observation system, such as the stereo endoscope, has been popularized in the field of medical treatment, notably surgery.
Originally, the technique of using a conventional endoscope and special treatment tools enables minimally invasive treatment to be received under the endoscope with respect to a disease that has required laparotomy. Furthermore, the endoscope has been designed so that a stereoscopic vision is possible, newly obtained information in a depth direction allows the treatment tool to be securely conducted into the human body, and a higher degree of finer treatment can be received in a shorter time than in the conventional endoscope. Consequently, it is expected that a surgical operation under the stereo endoscope which is a minimally invasive technique will be developed in the future.
In general, the stereo-observation system is of a binocular type, and as shown in FIG. 1, includes three units: a stereo imaging unit 2 incorporating imaging optical systems and image sensors to form left and right images of an observation object 1 with parallax, a stereo image signal processing unit 3 in which a stereoscopic image is produced by the image signals of the left and right images obtained from the stereo imaging unit 2, and a stereo display unit 4 displaying the produced stereoscopic image.
In the stereo-observation system, the images of the object are formed on the imaging surfaces of the image sensors by the imaging optical systems of the stereo imaging unit 2. In order to obtain the left and right images with parallax, various systems are used in the imaging optical systems. The left and light images obtained by the image sensors are transmitted as the image signals from the stereo imaging unit 2 to the stereo image signal processing unit 3. The stereo image signal processing unit 3 performs necessary signal processing in accordance with the stereo display unit 4 provided behind the unit 3. The stereo display unit 4 forms the left and right images on display elements on the basis of the stereoscopic image sent from the stereo image signal processing unit 3.
In order to separately transmit the left and right images to an observer's eyes, various systems are also used in the stereo display unit 4. As a typical example of the system of a stereo display apparatus, there is a virtual-image stereo-observation type in which light is projected directly on the left an right pupils (eyes) of the observer corresponding to the left and right images by optical systems located very close to the observer's face so that image information of a large image plane is equivalently thought of as a virtual image, which is observed stereoscopically.
A system combining the stereo endoscope with the virtual-image stereo-observation type of display apparatus has been proposed (refer to, for example, Japanese Patent Kokai No. Hie 8-313828). The stereo-observation system set forth in this publication establishes the relationship of the field angle between the stereo endoscope and the virtual-image stereo-observation type of display apparatus in order to observe the image of the stereo endoscope in a natural, virtual reality.
The stereo endoscope has a large depth of field like a common endoscope, which is not constructed for a stereoscopic vision, so that the object is captured in the range of the depth of field and is observed at a desired position by moving the stereo endoscope close to, or far away from, the object. The depth of field refers to the limit of an object distance in which the object can be observed without blurring. In the observation, focus adjustment and the adjustment of an angle of vergence, required in accordance with a distance from the stereo endoscope to the object are not made.
FIG. 2A shows this state. In this figure, reference numeral 5 denotes a stereo endoscope; 6, an endoscope holding arm; 7, a virtual-image stereo-observation type of display apparatus; 8, a display apparatus holding arm; and 9, an observer. FIG. 2B shows the enlargement of a distal end 10 of the stereo endoscope 5. Reference numeral 11 denotes an endoscope distal end; 12, a left-hand entrance pupil of a stereo endoscope optical system; 13, a right-hand entrance pupil of the stereo endoscope optical system; 14, an angle of vergence of the stereo endoscope; 15, a focal position of the stereo endoscope; 16, a range of the depth of field of the stereo endoscope; 17, an object located at a position A closest to the stereo endoscope in the range of the depth of field; 18, an object located at a focal position B of the stereo endoscope; and 19, an object located at a position C farthest away from the stereo endoscope in the range of the depth of field.
The observer 9 operates the stereo endoscope to move it backward and forward as mentioned above and captures and observes the object in the range from the position A to the position C. Observation images where the objects are located at the positions A-C are represented by reference numeral 20. Reference numeral 21 designates a pair of observation images when the object is located at the position A; 22, an observation image for the right eye; 23, an observation image for the left eye; and 24, center positions of individual observation images. Images 25 of the object are shifted inwardly from the center positions 24 of the observation images in both the left and right images. Reference numeral 22′ designates a pair of observation images when the object is located at the position B; 26, an observation image for the right eye; and 27, an observation image for the left eye. Images 28 of the object are located at the center positions 24 of the observation images in both the left and right images. Reference numeral 23′ designates a pair of observation images when the object is located at the position C; 29, an observation image for the right eye; and 30, an observation image for the left eye. Images 31 of the object are shifted outwardlyly from the center positions 24 of the observation images in both the left and right images. As mentioned above, the images of the object in the observation images are sometimes shifted inwardly or outwardly, depending on the distance between the stereo endoscope and the object.
In FIG. 3, reference numeral 32 represents a virtual-image stereo-observation type  of display apparatus; 33, an eyepiece optical system for the right eye; 34, an eye piece optical system for the left eye; 35, an image display means for the right eye; 36, an image display means for the left eye; 37, an image of the object shifted outwardly, displayed on the image display means for the right eye; 38, an image of the object shifted outwardly, displayed on the image display means for the left eye; and 29, an observer.
In the virtual-image stereo-observation type of display apparatus which previously has the angle of vergence of some degree, when the images of the object are mutually shifted inwardly, the lines of sight of the observer directed toward the left and right images of the object, as shown in FIG. 4, cross at a position fairly closer than numeral 40 denoting the positions of virtual images produced by the virtual-image stereo-observation type of display apparatus and also the focal positions of the eyes.
In FIG. 4, reference numeral 41 represents a virtual-image stereo-observation type of display apparatus; 42, an eyepiece optical system for the right eye; 43, an eye piece optical system for the left eye; 44, an image display means for the right eye; 45, an image display means for the left eye; 46, an image of the object shifted inwardly, displayed on the image display means for the right eye; 47, an image of the object shifted inwardly, displayed on the image display means for the left eye; 48, an observer; and 49, an intersection of the lines of sight of the observer directed toward the left and right images of the object. The eyepiece optical system 42 for the right eye and the eyepiece optical system 43 for the left eye are arranged to make an angle of vergence α.
As shown in FIGS. 5A and 5B, an object 1001 where it lies horizontally (FIG. 5A) and where it stands upright (FIG. 5B) are imaged by a stereo imaging apparatus 1000 at an angle of vergence α1. Subsequently, as shown in FIGS. 6A and 6B, when the object lying horizontally and the object standing upright, imaged by the stereo imaging apparatus, are observed through the stereo display apparatus which has an angle of vergence α2 appreciably smaller than the angle of vergence a α1 of the stereo imaging apparatus of FIG. 5A, an observation image 1002 of the object lying horizontally is considerably different in length visible to the eye from an observation image 1003 of the object standing upright. As mentioned above, in the stereo-observation system including the stereo imaging apparatus and the stereo display apparatus which are appreciably different in the angle of vergence from each other, the space of the object to be observed may be subjected to strong strain.